1. Field of the Invention
This invention is a universal reset circuit for digital circuitry which monitors both clock pulses and DC voltage and provides a reset command when detecting a low DC voltage or a missing clock pulse.
2. Description of the Prior Art
With the increased frequency of power brownouts and power interruptions, it is necessary to have a reliable circuit which can detect both a low DC voltage and a missing clock pulse and generate a reset command. The reset command would re-initialize a microprocessor chip or the input controller of a main computer system. Without such a reset circuit a brownout or power interruption in a peripheral device would necessitate an operator shutdown of the entire computer system.
Power brownouts and power interruptions can be of two types. They can be of a relatively long duration and produce a lowering of the DC voltage, or of a transient nature, resulting in a possible missed pulse in the clock circuit. A missed pulse in the clock circuit could also be produced by an EMI signal or by an electrostatic discharge. It is desirable to detect both a reduced DC voltage and a missed clock pulse.
Prior art devices fail to detect both a low DC voltage and a missed clock pulse. Some prior art devices concentrate on clock pulse failure and detection using complex multi-vibrator circuits or continuously comparing one clock with another clock in phase lock. Other prior art devices concentrate on protecting volatile memory from DC power interruptions. The prior art does not show a circuit which can detect both low DC voltage and a missed clock pulse and generate a reset pulse which is compatible with current microprocessor chips and input controllers.